Multi-element antenna beamforming in a wireless access network

ABSTRACT

A communication node of a wireless local area network utilizes a multi-element array antenna to estimate an angle-of-arrival for one or more signal sources which may communicate on symbol-modulated orthogonal subcarriers. Channel coefficients may be estimated from the angle-of-arrival for the one or more signal sources to increase channel capacity, improve channel equalization and reduce the effects of multipath fading. Beamforming based on the angle-of-arrival may also be performed for directional reception and/or transmission of communications with the one or more signal sources.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/654,037, filed Sep. 3, 2003, now issued as U.S. Pat. No. 7,453,946,which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention pertain to wireless communications,and some embodiments pertain to systems using symbol-modulatedorthogonal subcarrier communications.

BACKGROUND

Orthogonal frequency division multiplexing is an example of amulti-carrier transmission technique that uses symbol-modulatedorthogonal subcarriers to transmit information within an availablespectrum. When the subcarriers are orthogonal to one another, they maybe spaced much more closely together within the available spectrum than,for example, the individual channels in a conventional frequencydivision multiplexing (FDM) system. To achieve orthogonality, asubcarrier may have a null at the center frequency of the othersubcarriers. Orthogonality of the subcarriers may help reduceinter-subcarrier interference within the system. Before transmission,the subcarriers may be modulated with a low-rate data stream. Thetransmitted symbol rate of the symbols may be low, and thus thetransmitted signal may be highly tolerant to multipath delay spreadwithin the channel. For this reason, many modern digital communicationsystems are using symbol-modulated orthogonal subcarriers as amodulation scheme to help signals survive in environments havingmultipath reflections and/or strong interference.

Communication systems that use symbol-modulated orthogonal subcarriercommunications may have reduced channel capacity due to multipath fadingand other channel conditions. Thus, there are general needs forapparatus and methods that increase channel capacity, improve channelequalization and/or reduce the effects of multipath fading, especiallyin systems using symbol-modulated orthogonal subcarrier communications.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims are directed to some of the various embodiments ofthe present invention. However, the detailed description presents a morecomplete understanding of embodiments of the present invention whenconsidered in connection with the figures, wherein like referencenumbers refer to similar items throughout the figures and:

FIG. 1 illustrates a wireless communication environment in which someembodiments of the present invention may be practiced;

FIG. 2 is a block diagram of a communication node in accordance withsome embodiments of the present invention;

FIG. 3 illustrates a block diagram of a transceiver in accordance withsome embodiments of the present invention;

FIG. 4 illustrates a time-frequency structure of an orthogonal frequencydivision multiplexed packet suitable for use with some embodiments ofthe present invention; and

FIG. 5 is a flow chart of a communication procedure in accordance withsome embodiments of the present invention.

DETAILED DESCRIPTION

The following description and the drawings illustrate some specificembodiments of the invention sufficiently to enable those skilled in theart to practice them. Other embodiments may incorporate structural,logical, electrical, process, and other changes. Examples merely typifypossible variations. Individual components and functions are optionalunless explicitly required, and the sequence of operations may vary.Portions and features of some embodiments may be included in orsubstituted for those of others. The scope of embodiments of theinvention encompasses the full ambit of the claims and all availableequivalents of those claims.

FIG. 1 illustrates a wireless communication environment in which someembodiments of the present invention may be practiced. Communicationenvironment 100 includes one or more wireless communication devices(WCD) 102 which may communicate with access point (AP) 104 overcommunication links 108, which may be bi-directional links. WCDs 102 mayinclude, for example, personal digital assistants (PDAs), laptop andportable commuters with wireless communication capability, web tablets,wireless telephones, wireless headsets, pagers, instant messagingdevices, MP3 players, digital cameras, and other devices that mayreceive and/or transmit information wirelessly. WCDs 102 may communicatewith AP 104 using a multi-carrier transmission technique, such as anorthogonal frequency division multiplexing (OFDM) technique that usesorthogonal subcarriers to transmit information within an assignedspectrum. WCDs 102 and AP 104 may also implement one or morecommunication standards, such as one of the IEEE 802.11a, b or gstandards, the Digital Video Broadcasting Terrestrial (DVB-T)broadcasting standard, or the High performance radio Local Area Network(HiperLAN) standard. Other local area network (LAN) and wireless areanetwork (WAN) communication techniques may also be suitable forcommunication over links 108.

In addition to facilitating communications between WCDs 102, in someembodiments, AP 104 may be coupled with one or more networks 114, suchas an intranet or the Internet, allowing WCDs 102 to access suchnetworks. For convenience, the term “downstream” is used herein todesignate communications in the direction from AP 104 to WCDs 102 whilethe term “upstream” is used herein to designate communications in thedirection from WCDs 102 to AP 104, however, the terms downstream andupstream may be interchanged. WCDs 102 may support duplex communicationsutilizing different spectrum for upstream and downstream communications,although this is not a requirement. In some embodiments, upstream anddownstream communications may share the same spectrum for communicatingin both the upstream and downstream directions. Although FIG. 1illustrates point-to-multipoint communications, embodiments of thepresent invention are suitable to both point-to-multipoint andpoint-to-point communications.

In some embodiments, a communication node (e.g., access point 104) of awireless local area network (WLAN) may utilize multi-element arrayantenna 106 to estimate angle-of-arrival 110 (e.g., theta (θ)) forcommunication signals received over links 108 from one or more signalsources (e.g., WCDs 102). Angle 110 may be measured relative to end-firedirection 116 of the antenna 106, although the scope of the invention isnot limited in this respect. The signal sources may be wirelesscommunication devices which communicate on symbol-modulated orthogonalsubcarriers. Channel coefficients may be estimated from theangle-of-arrival for the one or more signal sources to increase channelcapacity, improve channel equalization and/or reduce the effects ofmultipath fading. In some embodiments, the channel coefficients may begenerated from one symbol modulated on a plurality of subcarriersreceived by different elements of antenna 106. In some embodiments, AP104 may provide communications within a range of up to 500 feet, andeven greater, for wireless communication devices, although the scope ofthe invention is not limited in this respect.

In some embodiments, beamforming coefficients may also be generated fromthe angle-of-arrival for improved reception and/or transmission ofcommunication signals with the one or more signal sources usingmulti-element array antenna 106. The beamforming coefficients may beused to direct the reception and/or transmission of signals in adirection of the particular signal source. The angle-of-arrival may beestimated by sampling the response from the antenna elements of thearray for at least one symbol at the subcarrier frequencies, althoughthe scope of the invention is not limited in this respect. The sampledsymbol may be a training symbol having a known value. The sampling maybe performed on the same symbol at all subcarrier frequencies afterdemodulation by a fast Fourier transform (FFT) although the scope of theinvention is not limited in this respect. With beamforming, frequencyreuse may be realized using space-division multiple access techniques.

Multi-element array antenna 106 may be a phased-array antenna comprisingat least two directional or omnidirectional antenna elements 112.Elements 112 may comprise dipole antennas, monopole antennas, loopantennas, microstrip antennas or other type of antenna suitable forreception and/or transmission of RF signals which may be processed by AP104. In some embodiments, a beamformer may be used to control phasingbetween elements 112 to provide directional communications with WCDs102. In some embodiments, the phasing may be controlled at baseband,although the scope of the invention is not limited in this respect.

FIG. 2 is a block diagram of a communication node in accordance withsome embodiments of the present invention. Communication node 200 may besuitable for use as AP 104 (FIG. 1), although other communication nodesmay also be suitable. In some embodiments, communication node 200 mayalso be suitable for use as one or more of WCDs 102 (FIG. 1), althoughthe scope of the invention is not limited in this respect.

Communication node 200 receives and/or transmits radio frequency (RF)communications with multi-element array antenna 202. RF signals receivedfrom antenna 202 may be converted to baseband signals and eventually todata signals comprising a bit stream by transceiver 204. Transceiver 204may also convert data signals comprising a bit stream to basebandsignals and RF signals for transmission by antenna 202. Communicationnode 200 may also include signal separator 206 to separate received andtransmitted communication signals. Communication node 200 may alsoinclude data processing portion 208 to process data signals receivedthrough transceiver 204 and generate data signals for transmission bytransceiver 204. Antenna 202 may comprise a plurality of antennaelements 212, which may correspond to antenna elements 112 (FIG. 1).Although signal separator 206 is illustrated as a separate element ofnode 200, the present invention is not limited in this respect. In someembodiments, signal separator 206 may be part of antenna 202, while inother embodiments, antenna 202 may comprise one set of antenna elementsfor transmission of signals, and another set of antenna elements forreception of signals eliminating the need for signal separator 206.

In some embodiments, communication node 200 may include interfaces 210to wireline devices and wireline networks, such as to a personalcomputer, a server, or the Internet, for example. In these embodiments,communication node 200 may facilitate communications between WCDs 102(FIG. 1) and these wireline devices and/or networks.

FIG. 3 illustrates a block diagram of a transceiver in accordance withsome embodiments of the present invention. Transceiver 300 may besuitable for use as transceiver 204 (FIG. 2) although other transceiverconfigurations may also be suitable. Transceiver 300 may include RFcircuitry 302 to receive a signal from a signal source through amulti-element antenna having a plurality of antenna elements. The signalmay comprise a plurality of subcarriers modulated with at least onesymbol. Transceiver 300 may also include angle-of-arrival (AOA)estimator 304 to estimate an angle-of-arrival for a signal source from asubcarrier level of the symbol received by at least two of the antennaelements. Transceiver 300 may also include channel coefficient generator306 to generate channel coefficients for communications received fromthe signal source based on the angle-of-arrival. The channelcoefficients may compensate for at least some of the channel effectsbetween a signal source and the access point. Transceiver 300 may alsoinclude channel equalizer 308 which may be responsive to the channelcoefficients to provide equalized frequency-domain symbol-modulatedsubcarriers 310 resulting in improved reception.

In some embodiments, transceiver 300 may further include beamformercoefficient generator 312 to generate beamforming coefficients forelements of the multi-element antenna based on the angle-of-arrival. Thebeamforming coefficients may be used to help direct the reception and/ortransmission of signals in a direction of a particular signal source. Inthese embodiments, transceiver 300 may further include beamformer 314.Beamformer 314 may change the directionality of the antenna based on thebeamforming coefficients, and in some embodiments, beamformer 314 maychange phasing of received and/or transmitted signals. In someembodiments, beamforming may be done prior to conversion tocorresponding RF signals by RF circuitry 302 and transmission of thesignals by the elements of the multi-element antenna. In someembodiments, beamformer 314 may change the directionality of the antennaby changing the phasing of baseband-level signals that comprise aplurality of symbol-modulated subcarriers for use in generating and/orreceiving an orthogonal-frequency division multiplexed signal by RFcircuitry 302 for transmission and/or reception by a multi-elementantenna. With beamforming, frequency reuse may be realized usingspace-division multiple access techniques.

In some embodiments, angle-of-arrival estimator 304 may include one ormore processors and memory to generate an initial matrix (e.g., X)comprising demodulated pilot subcarriers for a symbol provided by FFT328 corresponding to each of the antenna elements. The processor andmemory may also generate a response matrix (e.g., A) substantially fromthe equation X=AD+N. In the equation, ‘D’ may represent a diagonalmatrix having elements corresponding to the pilot subcarriers of thesymbol, and ‘N’ may represent an uncorrelated noise matrix. Theprocessor and memory may use a search function to identify a peakcorresponding to the angle-of-arrival. The search function may be basedon a decomposition of the response matrix. This is described in moredetail below.

FIG. 4 illustrates a time-frequency structure of an orthogonal frequencydivision multiplexed packet suitable for use with some embodiments ofthe present invention. Time-frequency structure 400 is an example of apacket in accordance with the IEEE 802.11(a) standard; however, othertime-frequency structures for packets may be equally suitable for usewith some embodiments of the present invention. As illustrated instructure 400, symbols having known training values arecrosshatched/shaded. Structure 400 illustrates a packet starting withten short training symbols 402 modulated on twelve subcarriers 404.These symbols may contain known pilot subcarriers. Short trainingsymbols 402 are followed by two long training symbols 406 which arefollowed by data symbols 408. Data symbols 408 may include four pilotsubcarriers 410.

In some embodiments, angle-of-arrival estimator 304 (FIG. 3) mayestimate the angle-of-arrival based the antenna response for subcarriers404 for one of training symbols 402 or based on one of training symbols406, although the scope of the invention is not limited in this respect.A training symbol may have known training values. In some embodiments,channel equalizer 308 (FIG. 3) may provide equalized frequency-domainsymbol-modulated subcarriers for subsequent data symbols (e.g., symbols408) of a data packet received from the signal source.

Referring back to FIG. 3, in some embodiments, RF receive circuitry 302receives signals through a multi-element antenna, and generates serialsymbol stream 320 representing symbols. In some embodiments, a packetmay include short training symbols 402 (FIG. 4) and long trainingsymbols 406 (FIG. 4) followed by data symbols 408 (FIG. 4). In someembodiments, the received signal may have a carrier frequency rangingbetween 5 and 6 GHz, although embodiments of the present invention areequally suitable to carrier frequencies, for example, ranging between 2and 20 GHz, and even greater. In some embodiments, a symbol-modulatedsignal may include up to a hundred or more subcarriers. The shorttraining symbols may be transmitted on a portion of the subcarriers, anddata symbols may contain one or more known pilot subcarriers althoughthis is not a requirement. In some embodiments, the long trainingsymbols may have a duration of approximately 4 microseconds and theshort training symbols may have a duration of approximately onemicrosecond. In some embodiments, the signals may be infrared (IR)signals.

The receiver portion of transceiver 300 may include serial to parallel(S/P) converter 322 to convert a symbol of serial symbol stream 320 intoparallel groups of time-domain samples 324. Cyclic-redundancy prefix(C/P) element 326 removes a cyclic-redundancy prefix from each symbol.Fast Fourier Transform (FFT) element 328 performs an FFT on parallelgroups of time-domain samples 330 to generate frequency-domainsymbol-modulated subcarriers 332 for use by equalizer 308 andangle-of-arrival estimator 304.

Angle-of-arrival estimator 304 may generate an angle-of-arrival estimatefor a signal source which may be used by channel coefficient generator306 for generating channel coefficients for use by equalizer 308 forimproved demodulation of the subcarriers. In some embodiments, a channelestimator (not illustrated) may be used, in addition to generator 306,to generate channel estimates for use by equalizer 308.

Equalizer 308 may perform a channel equalization on frequency-domainsymbol-modulated subcarriers 332 provided by FFT element 328. Equalizer308 may generate equalized frequency-domain symbol-modulated subcarriers310 using the channel coefficients provided by channel coefficientgenerator 306. For example, equalization in the frequency domain may beperformed by division of the frequency domain subcarriers 332 withcomplex values that represent the channel estimation. Accordingly, themagnitudes of equalized frequency-domain symbol-modulated subcarriers332 may be normalized and the phases of equalized frequency-domainsymbol-modulated subcarriers 310 may be aligned to a zero origin toallow for further processing by demapper 334.

Equalized frequency-domain symbol-modulated subcarriers 310 may bedemapped by demapper 334 to produce a plurality of parallel symbols.Demapper 334 may demap the parallel symbols in accordance with aparticular modulation order in which the transmitter modulated thesubcarriers. Modulation orders, for example, may include binary phaseshift keying (BPSK), which communicates one bit per symbol, quadraturephase shift keying (QPSK), which communicates two bits per symbol,8-PSK, which communicates three bits per symbol, 16-quadrature amplitudemodulation (16-QAM), which communicates four bits per symbol, 32-QAM,which communicates five bits per symbol, and 64-QAM, which communicatessix bits per symbol. Modulation orders may also includedifferentially-coded star QAM (DSQAM). Modulation orders with lower andeven higher communication rates may also be used. The parallel symbolsfrom demapper 334 may be converted from a parallel form to a serialstream by parser 336, which may perform a de-interleaving operation onthe serial stream. Parser 336 generates decoded serial bit stream 338for use by data processing elements (not illustrated).

The transmitter portion of transceiver 300 may include parser 342 toencode serial bit-stream 340 to generate parallel symbols. Mapper 344maps the parallel symbols to frequency-domain symbol-modulatedsubcarriers 346. IFFT element 348 performs an inverse fast Fouriertransform (IFFT) on frequency-domain symbol-modulated subcarriers 346 togenerate parallel groups of time-domain samples 350. CP circuit 352 addsa cyclic-redundancy prefix to each symbol, and parallel-to-serial (P/S)circuit 354 converts the parallel groups of time-domain samples 356 toserial symbol stream 358 for RF circuitry 302. In accordance withembodiments, the length of the cyclic-redundancy prefix is greater thanthe length of intersymbol interference.

Although communication node 200 (FIG. 2) and transceiver 300 areillustrated as having several separate functional circuit elements, oneor more of the functional elements may be combined and may beimplemented by combinations of software-configured elements, such asprocessing elements including digital signal processors (DSPs), and/orother hardware elements and software. For example, circuit elements maycomprise one or more processing elements such as microprocessors, DSPs,application specific integrated circuits (ASICs), and combinations ofvarious hardware and logic circuitry for performing at least thefunctions described herein.

FIG. 5 is a flow chart of a communication procedure in accordance withsome embodiments of the present invention. Communication procedure 500may be performed by a communication node, such as AP 104 (FIG. 1)although other communication nodes may also be suitable for performingprocedure 500. In some embodiments, communication procedure 500 may beperformed by communication devices, such as WCDs 102 (FIG. 1). Althoughthe individual operations of procedure 500 are illustrated and describedas separate operations, one or more of the individual operations may beperformed concurrently and nothing requires that the operations beperformed in the order illustrated.

In operation 502, a signal comprising at least one symbol of a datapacket comprising symbol-modulated subcarriers is received through amulti-element antenna from a signal source. In operation 504, an FFT maybe performed on parallel groups of time-domain samples that representthe symbol as received by the elements of the multi-element antenna. TheFFT may generate frequency-domain symbol-modulated subcarriers for eachantenna element. The symbol may be a training symbol having knowntraining values. In operation 506, an angle-of-arrival estimate isgenerated for the signal source. The angle-of-arrival may be relative toan end-fire direction of the multi-element antenna. The angle-of arrivalmay be estimated based on the antenna response for the antenna elementsfor more than one subcarrier frequency of the symbol, although the scopeof the invention is not limited in this respect. In operation 508,channel coefficients may be generated from the angle-of-arrivalestimate, and in operation 510, the channel coefficients may be used forequalization of symbols, including data symbols, subsequently receivedfrom the signal source. In operation 512, beamforming coefficients maybe generated based on the angle-of arrival, and in operation 514, acommunication signal comprising symbol-modulated subcarriers may bedirectionally transmitted to the signal source (e.g., in a direction ofthe signal source) using the beamforming coefficients. In someembodiments, a communication signal comprising symbol-modulatedsubcarriers may be directionally received from the signal source usingthe beamforming coefficients.

In some embodiments, the operations of procedure 500 may be repeated orperformed concurrently for one or more of a plurality of signal sources.In these embodiments, angles-of-arrival may be individually estimatedfor the different signal sources, and channel and beamformingcoefficients may be generated for the different signal sources and usedfor communicating with the signal sources. Accordingly, increasedchannel capacity, improved channel equalization and/or reduced theeffects of multipath fading may be achieved, although the scope of theinvention is not limited in this respect.

In some embodiments of the present invention, an angle-of-arrival may beestimated by angle-of-arrival estimator 304 (FIG. 2) and channelcoefficients may be generated by channel coefficient generator 306 (FIG.3) as illustrated in the following example. Consider an N-elementadaptive antenna receiving J− user signals having J distinct directionsθ₁, . . . θ_(J), where the angles θ_(j) are measured with respect toend-fire direction 116 (FIG. 1). In this example, let Q be number ofsubcarriers used to carry known pilot subsymbols transmission. Theremaining (K-Q) subcarriers may be used for information bearingsubsymbols. In this example, consider N>Q. For the sake of generality, asingle sample case is illustrated which may be further extended formultiple samples in which an average estimate may be obtained. In thesingle-sample case, the signals may be collected after demodulation byan FFT in the form of matrix, which may be described by the followingequations.X=AD+N  (1)

In equation (1), X is a matrix in which the i^(th) column may correspondto the antenna-array response to the i^(th) subcarrier. D is a diagonalmatrix whose elements may correspond to the known pilot symbols scaledby channel coefficients along with the phase shift. A is anarray-response matrix for the subcarrier frequencies. m corresponds tothe m th symbol. N may be a spatially and temporally uncorrelated noisematrix.

$\begin{matrix}{X = \begin{bmatrix}{x_{1}( {m,0} )} & {x_{1}( {m,1} )} & \ldots & {x_{1}( {m,{Q - 1}} )} \\{x_{2}( {m,0} )} & {x_{2}( {m,1} )} & \ldots & {x_{2}( {m,{Q - 1}} )} \\\ldots & \ldots & \ldots & \ldots \\{x_{N}( {m,0} )} & {x_{N}( {m,1} )} & \ldots & {x_{N}( {m,{Q - 1}} )}\end{bmatrix}} & (2) \\{A = \begin{bmatrix}1 & 1 & \ldots & 1 \\{\mathbb{e}}^{{\mathbb{i}}\; k_{1}d\;\cos\;\theta} & {\mathbb{e}}^{{\mathbb{i}}\; k_{2}d\;\cos\;\theta} & \ldots & {\mathbb{e}}^{{\mathbb{i}}\; k_{Q}d\;\cos\;\theta} \\\ldots & \ldots & \ldots & \ldots \\{\mathbb{e}}^{{\mathbb{i}}\; k_{1}{d{({N - 1})}}\cos\;\theta} & {\mathbb{e}}^{{\mathbb{i}}\; k_{2}{d{({N - 1})}}\cos\;\theta} & \ldots & {\mathbb{e}}^{{\mathbb{i}}\; k_{Q}{d{({N - 1})}}\cos\;\theta}\end{bmatrix}} & (3)\end{matrix}$D=diag(p(m,0),p(m,1), . . . , p(m,Q−1))  (4)p(m,0)=s(m,0)h ₀ e ^(−iδ) ¹ , . . . , p(m,Q−1)=s(m,Q−1)^(h) _(Q-1) e^(−iδ) ^(Q-1)   (5)

$\begin{matrix}{N = \begin{bmatrix}{n_{11}( {m,0} )} & {n_{12}( {m,0} )} & \ldots & {n_{1Q}( {m,0} )} \\{n_{21}( {m,0} )} & {n_{22}( {m,0} )} & \ldots & {n_{2Q}( {m,0} )} \\\ldots & \ldots & \ldots & \ldots \\{n_{N\; 1}( {m,0} )} & {n_{N\; 2}( {m,0} )} & \ldots & {n_{NQ}( {m,0} )}\end{bmatrix}} & (6)\end{matrix}$

In some embodiments, equation (1) may be multiplied by unit vectors,e.g., e=[1 . . . 1]^(T) and shown as Xe=ADe+Ne which reduces to:x=Ap  (7)where x=x₁+x₂+ . . . +x_(Q-1) and p=p₁+p₂+ . . . +p_(Q-1)xεspan{A}  (8)

A matrix B may be formed.B=[A(θ)x] where θε(0,2π).  (9)

The size of matrix B may be N(Q+1), where N≧(Q+1).

Matrix B may become rank deficient (e.g., undetermined) when θ=θ_(true).The θ_(true) estimate can be found from the following QR-decompositionand search function.B(θ)=Q(θ)R(θ),  (10)with search function as

$\begin{matrix}{{G(\theta)} = {{\max\lbrack \frac{1}{r_{{(Q)}{(Q)}}(\theta)} \rbrack}.}} & (11)\end{matrix}$

r_(Q,Q)(θ) is the Q-th diagonal element of the upper triangular matrixR(θ). The search function G(θ) may have J-highest peaks that maycorrespond to the angle-of-arrival estimates, {circumflex over (θ)}₁, .. . . {circumflex over (θ)}_(J) of J-sources. Note that the estimates({circumflex over (θ)}₁, . . . {circumflex over (θ)}_(J)) may beobtained from processing of four pilot subcarriers that are spaced quiteapart in the frequency spectrum. Such a property may provide a goodapproximation of the angle-of-arrival corresponding to the complete setof subcarriers in the OFDM. In other words the estimates may correspondto angle-of arrival of broadband signal sources.

Having obtained {circumflex over (θ)}ε({circumflex over (θ)}₁, . . .{circumflex over (θ)}_(J)), {circumflex over (θ)} may be substituted inthe matrix A in equation (7) as{circumflex over (x)}=A({circumflex over (θ)})p.  (12)

Thus, in equation (12) p remains unknown, and may be obtained asfollows:p=[A({circumflex over (θ)})A({circumflex over (θ)})]⁻¹ A^(T)({circumflex over (θ)})x.  (13)

The k th element of p is p(m,k)=s(m,k)h_(k)e^(−iδ) ^(k) . Since s(m,k)is known, the channel estimation may be obtained as

$\begin{matrix}{{h_{k}{\mathbb{e}}^{- {\mathbb{i}\delta}_{k}}} = \frac{p( {m,k} )}{s( {m,k} )}} & (14)\end{matrix}$

where s(m,k), k=1, . . . , Q are known pilot symbols.

In the second stage, the next set of Q-subcarriers may be chosen toobtain the channel coefficients as,p=[A({circumflex over (θ)})A({circumflex over (θ)})]⁻¹ A^(T)({circumflex over (θ)})x,

where A({circumflex over (θ)}) corresponds to the columns as a functionof next subset of subcarriers. This channel estimation process may berepeated for this next subset of subcarriers.

In some embodiments, the estimation of angular information {circumflexover (θ)} of a signal source may be performed for only one sample. Theangular estimate {circumflex over (θ)} may be repeatedly used for eachsubset of subcarrier matrices and accordingly the channel estimates forentire subcarrier channels may be found. For increased reliability, insome embodiments, the angular estimation may be performed for eachsample and the average estimate can be obtained as follows:θ_(estimate)=E[{circumflex over (θ)}].  (15)

In some embodiments, beamforming in the direction θ_(estimate) isperformed to increase the channel capacity. With beamforming, frequencyreuse may be realized using space-division multiple access techniques.The beamforming may be used for both reception and transmission.

It is emphasized that the Abstract is provided to comply with 37 C.F.R.Section 1.72(b) requiring an abstract that will allow the reader toascertain the nature and gist of the technical disclosure. It issubmitted with the understanding that it will not be used to limit orinterpret the scope or meaning of the claims.

In the foregoing detailed description, various features are occasionallygrouped together in a single embodiment for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the subjectmatter require more features that are expressly recited in each claim.Rather, as the following claims reflect, inventive subject matter liesin less than all features of a single disclosed embodiment. Thus thefollowing claims are hereby incorporated into the detailed description,with each claim standing on its own as a separate preferred embodiment.

1. A multicarrier transceiver for communicating orthogonal frequencydivision multiplexed (OFDM) signals in a wireless multiple accessnetwork over a plurality of space-division multiple access (SDMA)communication channels with a multi-element array antenna, thetransceiver comprising: a beamformer coefficient generator to generatebeamforming coefficients based on channel characteristics; and abeamformer to apply the beamforming coefficients to groups of one ormore subcarriers of a set of a plurality of subcarriers that comprisethe OFDM signals to control phasing between elements of themulti-element array antenna for communicating through two or more SDMAcommunication channels, each of the two or more SDMA communicationchannels to concurrently convey separate data streams over the set ofsubcarriers.
 2. The multicarrier transceiver of claim 1 furthercomprising RF circuitry coupled to the multi-element array antenna togenerate RF signals for transmission from baseband signals provided bythe beamformer, the RF signals being directed toward one or more signalssources.
 3. A method for communicating orthogonal frequency divisionmultiplexed (OFDM) signals in a wireless multiple access network over aplurality of space-division multiple access (SDMA) communicationchannels with a multi-element array antenna, the method comprising:generating beamforming coefficients based on received training signals;and applying the beamforming coefficients to groups of one or moresubcarriers of a set of a plurality of subcarriers that comprise theOFDM signals to control phasing between elements of the multi-elementarray antenna for communicating through two or more SDMA communicationchannels, each of the two or more SDMA communication channels toconcurrently convey separate data streams over the set of subcarriers.4. The method of claim 3 further comprising: generating RF signals fortransmission by the multi-element array antenna from baseband signalsprovided by the beamformer; and directing the RF signals toward one ormore signals sources.
 5. A method for beamforming in a wireless accessnetwork that communicates using orthogonal frequency divisionmultiplexed (OFDM) communication signals over a plurality ofspace-division multiple access (SDMA) channels, the method comprising:receiving OFDM training symbols over the spatial channels through aplurality of associated antennas, each of the associated antennascomprising elements of a multi-element array antenna; generating channelestimates for the spatial channels based on receipt of the trainingsymbols; and generating beamforming coefficients based on the channelestimates and applying the beamforming coefficients to groups of one ormore subcarriers of a set of a plurality of individual subcarriers thatcomprise OFDM signals for subsequent communications, wherein thebeamforming coefficients are applied at baseband to control phasingbetween elements of the multi-element array antenna, and wherein theassociated antennas that comprise elements of the multi-element arrayantenna are configured for communicating through two or more SDMAcommunication channels, each of the two or more SDMA communicationchannels to concurrently convey separate data streams over the set ofsubcarriers.
 6. The method of claim 5 further comprising: generating thebeamforming coefficients for the groups of subcarriers based on receivedtraining signals; and transmitting RF signals toward one or more signalssources.